Planetary gear train of automatic transmission for a vehicle

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque of the engine, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, and seven friction elements disposed to selectively connect the rotation elements with each other and selectively connect the rotation elements with a transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0078000 filed Jun. 2, 2015, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for avehicle. More particularly, the present invention relates to a planetarygear train for an automatic transmission of a vehicle that improvespower delivery performance and fuel efficiency as a consequence ofachieving ten forward speed stages using a minimum number of constituentelements, enlarging a span of gear ratios, and almost linearlyincreasing or decreasing step ratios between transmission steps.

Description of Related Art

In recent years, increasing oil prices have forced auto manufacturersinto extreme competition in order to enhance fuel efficiency.

As a result, research is being conducted on engines in terms of reducingweight and improving fuel efficiency by down-sizing, and research isalso being conducted to ensure both drivability and competitiveness formaximizing fuel efficiency by implementing an automatic transmissionwith multiple speed stages.

However, in the automatic transmission, as a number of transmissionspeed stages increases, the number of internal components increases, andas a result, the automatic transmission may be difficult to mount, themanufacturing cost and weight may be increased, and power transmissionefficiency may be deteriorated.

Accordingly, development of a planetary gear train which may bring aboutmaximum efficiency with a small number of components may be important inorder to increase a fuel efficiency enhancement effect through themultiple speed stages.

In this aspect, in recent years, 8-speed automated transmissions havetended to be achieved, and the research and development of a planetarygear train capable of implementing more transmission steps have alsobeen actively conducted.

Since a span of gear ratios of the recent 8-speed automatic transmissionis merely 6.5 to 7.5, the 8-speed automatic transmission has no greateffect of improving fuel efficiency.

In addition, since step ratios between transmission steps may not beincreased or decreased linearly in a case in which a span of shiftratios of the 8-speed automatic transmission is greater than or equal to9.0, driving efficiency of an engine and drivability of a vehicle may bedeteriorated. Accordingly, there is a need for development of a highlyefficient automatic transmission with 9 or more forward speed stages.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission for a vehicle thatimproves power delivery performance and fuel efficiency by achieving tenforward speed stages and two reverse speed stages using a minimum numberof constituent elements, by enlarging a span of gear ratios, and byalmost linearly increasing or decreasing step ratios betweentransmission steps.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, and seven friction elements disposed to selectivelyconnect the rotation elements with each other and selectively connectthe rotation elements with a transmission housing, in which the inputshaft may be continuously connected to the first rotation element, theoutput shaft may be continuously connected to the eleventh rotationelement, the third rotation element may be continuously connected to thefifth rotation element, the sixth rotation element may be continuouslyconnected to the seventh rotation element, the eighth rotation elementmay be continuously connected to the eleventh rotation element, theninth rotation element may be continuously connected to the tenthrotation element, and three friction elements among seven frictionelements are operated at each speed stage.

The second rotation element may be selectively connected to thetransmission housing, the fourth rotation element may be selectivelyconnected to the transmission housing, the ninth rotation element may beselectively connected to the transmission housing, the fourth rotationelement may be selectively connected to the output shaft, the twelfthrotation element may be selectively connected to the input shaft, andthe sixth rotation element may be selectively connected to the secondrotation element.

The first, second, and third rotation elements of the first planetarygear set may be a sun gear, a planet carrier, and a ring gear, thefourth, fifth, and sixth rotation elements of the second planetary gearset may be a sun gear, a planet carrier, and a ring gear, the seventh,eighth, and ninth rotation elements of the third planetary gear set maybe a sun gear, a planet carrier, and a ring gear, and the tenth,eleventh, and twelfth rotation elements of the fourth planetary gear setare a sun gear, a planet carrier, and a ring gear.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, and seven friction elements disposed to selectivelyconnect the rotation elements with each other and selectively connectthe rotation elements with a transmission housing, a first rotationshaft including the first rotation element and directly connected to theinput shaft, a second rotation shaft including the second rotationelement and selectively connected to the first rotation shaft and thetransmission housing, a third rotation shaft including the third andfifth rotation elements, a fourth rotation shaft including the fourthrotation element and selectively connected to the transmission housing,a fifth rotation shaft including the sixth and seventh rotation elementsand selectively connected to the second rotation shaft, a sixth rotationshaft including the eighth and eleventh rotation elements andselectively connected to the fourth rotation shaft, and directlyconnected to the output shaft, a seventh rotation shaft including theninth and tenth rotation elements and selectively connected to thetransmission housing, and an eighth rotation shaft including the twelfthrotation element and selectively connected to the input shaft.

The first planetary gear set may be a single-pinion planetary gear set,in which the first rotation element may be a first sun gear, the secondrotation element may be a first planet carrier, and the third rotationelement may be a first ring gear, the second planetary gear set may be asingle-pinion planetary gear set, in which the fourth rotation elementmay be a second sun gear, the fifth rotation element may be a secondplanet carrier, and the sixth rotation element may be a second ringgear, the third planetary gear set may be a single-pinion planetary gearset, in which the seventh rotation element may be a third sun gear, theeighth rotation element may be a third planet carrier, and the ninthrotation element may be a third ring gear, and the fourth planetary gearset may be a single-pinion planetary gear set, the tenth rotationelement may be a fourth sun gear, the eleventh rotation element may be afourth planet carrier, and the twelfth rotation element may be a fourthring gear.

The seven friction elements may include a first clutch selectivelyconnecting the fourth and sixth rotation shafts, a second clutchselectively connecting the first and second rotation shafts, a thirdclutch selectively connecting the input shaft and the eighth rotationshaft, a fourth clutch selectively connecting the second and fifthrotation shafts, a first brake selectively connecting the seventhrotation shaft and the transmission housing, a second brake selectivelyconnecting the second rotation shaft and the transmission housing, and athird brake selectively connecting the fourth rotation shaft and thetransmission housing.

Shift speed stages achieved by selectively operating the seven frictionelements may include a first forward speed stage achieved bysimultaneous operation of the fourth clutch and the first and thirdbrakes, a second forward speed stage achieved by simultaneous operationof the second and fourth clutches and the first brake, a third forwardspeed stage achieved by simultaneous operation of the second clutch andthe first and third brakes, a fourth forward speed stage achieved bysimultaneous operation of the third clutch and the first and thirdbrakes, a fifth forward speed stage achieved by simultaneous operationof the second and third clutches and the third brake, a sixth forwardspeed stage achieved by simultaneous operation of the second, third andfourth clutches, a seventh forward speed stage achieved by simultaneousoperation of the third and fourth clutches and the third brake, aneighth forward speed stage achieved by simultaneous operation of thethird and fourth clutches and the second brake, a ninth forward speedstage achieved by simultaneous operation of the third clutch and thesecond and third brakes, a tenth forward speed stage achieved bysimultaneous operation of the first and third clutch and the secondbrake, a first reverse speed stage achieved by simultaneous operation ofthe first, second, and third brakes, and a second reverse speed stageachieved by simultaneous operation of the first clutch and the first andsecond brakes.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, a first rotation shaft including the first rotationelement and directly connected to the input shaft, a second rotationshaft including the second rotation element and selectively connected tothe first rotation shaft and the transmission housing, a third rotationshaft including the third and fifth rotation elements, a fourth rotationshaft including the fourth rotation element and selectively connected tothe transmission housing, a fifth rotation shaft including the sixth andseventh rotation elements and selectively connected to the secondrotation shaft, a sixth rotation shaft including the eighth and eleventhrotation elements and selectively connected to the fourth rotationshaft, and directly connected to the output shaft, a seventh rotationshaft including the ninth and tenth rotation elements and selectivelyconnected to the transmission housing, an eighth rotation shaftincluding the twelfth rotation element and selectively connected to theinput shaft, a first clutch selectively connected to fourth and sixthrotation shafts, a second clutch selectively connected to the first andsecond rotation shafts, a third clutch selectively connected to theinput shaft and the eighth rotation shaft, a fourth clutch selectivelyconnected to the second and fifth rotation shafts, a first brakeselectively connected to the seventh rotation shaft and the transmissionhousing, a second brake selectively connected to the second rotationshaft and the transmission housing, and a third brake selectivelyconnected to the fourth rotation shaft and the transmission housing.

Various embodiments of the present invention may achieve ten forwardspeed stages and two reverse speed stages by combining four planetarygear sets that are simple planetary gear sets with seven frictionelements.

In addition, engine driving efficiency may be maximized by achieving aspan of shift ratios to be greater than or equal to 9.0.

Further, drivability such as acceleration before and after the shift andrhythm of engine speed may be improved by almost linearly increasing ordecreasing stage ratios between transmission stages.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an exemplary planetary gear trainaccording to the present invention.

FIG. 2 is an operation table for each of transmission steps ofrespective friction elements applied to the exemplary planetary geartrain according to the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

FIG. 1 is a configuration diagram of a planetary gear train according tovarious embodiments of the present invention.

Referring to FIG. 1, the planetary gear train according to variousembodiments of the present invention includes first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on the sameaxis, and an input shaft IS, an output shaft OS, eight rotation shaftsTM1 to TM8 directly connecting to each other through respective rotationelements of the first, second, third, and fourth planetary gear setsPG1, PG2, PG3, and PG4, seven friction elements C1 to C4 and B1 to B3,and a transmission housing H.

As a result, torque input from the input shaft IS is transmitted by aninter-complementation operation of the first, second, third, and fourthplanetary gear sets PG1, PG2, PG3, and PG4 to be output through theoutput shaft OS.

The respective simple planetary gear sets are disposed in a sequence ofthe first, second, third, and fourth planetary gear sets PG1, PG2, PG3,and PG4 from an engine side.

The input shaft IS is an input member, and rotational power from acrankshaft of an engine is torque-converted through a torque converterto be input into the input shaft IS.

The output shaft OS is an output member, is disposed on the same axis asthe input shaft IS, and transfers transmitted driving torque to adriving shaft through a differential apparatus.

The first planetary gear set PG1 as a single-pinion planetary gear setincludes a first sun gear S1 which is a first rotation element N1, afirst planetary carrier PC1 which is a second rotation element N2 thatsupports a first pinion P1 which outer-engages with the first sun gearS1 which is the first rotation element N1, and a first ring gear R1which is a third rotation element N3 which inner-engages with the firstpinion P1 as rotation elements.

The second planetary gear set PG2 as a single-pinion planetary gear setincludes a second sun gear S2 which is a fourth rotation element N4, asecond planet carrier PC2 which is a fifth rotation element N5 thatsupports a second pinion P2 which outer-engages with the second sun gearS2 which is the fourth rotation element N4, and a second ring gear R2which is a sixth rotation element N6 which inner-engages with the secondpinion P2 as rotation elements.

The third planetary gear set PG3 as a single-pinion planetary gear setincludes a third sun gear S3 which is a seventh rotation element N7, athird planet carrier PC3 which is an eighth rotation element N8 thatsupports a third pinion P3 which outer-engages with the third sun gearS3 which is the seventh rotation element N7, and a third ring gear R3which is a ninth rotation element N9 which inner-engages with the thirdpinion P3 as the rotation elements.

The fourth planetary gear set PG4 as a single-pinion planetary gear setincludes a fourth sun gear S4 which is a tenth rotation element N10, afourth planet carrier PC4 which is an eleventh rotation element N11 thatsupports a fourth pinion P4 which outer-engages with the fourth sun gearS4 which is the tenth rotation element N10, and a fourth ring gear R4which is a twelfth rotation element N12 which inner-engages with thefourth pinion P4 as the rotation elements.

In the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4, the third rotation element N3 is directly connected to thefifth rotation element N5, the sixth rotation element N6 is directlyconnected to the seventh rotation element N7, the eighth rotationelement N8 is directly connected to the eleventh rotation element N11,and the ninth rotation element N9 is directly connected to the tenthrotation element N10 so as to be operated with a total of eight rotationshafts TM1 to TM8.

Configurations of the eight rotation shafts TM1 to TM8 will be describedbelow.

The first rotation shaft TM1 includes the first rotation element N1 (thefirst sun gear S1), and is directly connected to the input shaft IS soas to continuously be operated as an input element.

The second rotation shaft TM2 includes the second rotation element N2(the first planet carrier PC1), and is selectively connected to thefirst rotation shaft TM1 and the transmission housing H.

The third rotation shaft TM3 includes the third rotation element N3 (thefirst ring gear R1) and the fifth rotation element N5 (the second planetcarrier PC2).

The fourth rotation shaft TM4 includes the fourth rotation element N4(the second sun gear S2), and is selectively connected to thetransmission housing H.

The fifth rotation shaft TM5 includes the sixth rotation element N6 (thesecond ring gear R2) and the seventh rotation element N7 (the third sungear S3), and is selectively connected to the second rotation shaft TM2.

The sixth rotation shaft TM6 includes the eighth rotation element N8(the third planet carrier PC3) and the eleventh rotation element N11(the fourth planet carrier PC4), and is selectively connected to thefourth rotation shaft TM4 and is directly connected to the output shaftOS so as to continuously be operated as an output element.

The seventh rotation shaft TM7 includes ninth rotation element N9 (thethird ring gear R3) and the tenth rotation element N10 (the fourth sungear S4), and is selectively connected to the transmission housing H.

The eighth rotation shaft TM8 includes the twelfth rotation element N12(the fourth ring gear R4) and is selectively connected to the inputshaft IS.

In addition, among the rotation shafts TM1 to TM8, four clutches C1, C2,C3, and C4 which are friction elements are disposed at connectionportions where the rotation shafts are connected to each other.

In addition, among the rotation shafts TM1 to TM8, three brakes B1, B2,and B3 which are friction elements are disposed at connection portionsbetween any one rotation shaft and the transmission housing H.

The seven friction elements C1 to C4 and B1 to B3 will be described infurther detail.

The first clutch C1 is disposed between the fourth rotation shaft TM4and the sixth rotation shaft TM6, and selectively connects the fourthrotation shaft TM4 and the sixth rotation shaft TM6.

The second clutch C2 is disposed between the first rotation shaft TM1and the second rotation shaft TM2, and selectively connects the firstrotation shaft TM1 and the second rotation shaft TM2.

The third clutch C3 is disposed between the input shaft IS and theeighth rotation shaft TM8, and selectively connects the input shaft ISand the eighth rotation shaft TM8.

The fourth clutch C4 is disposed between the second rotation shaft TM2and the fifth rotation shaft TM5, and selectively connects the secondrotation shaft TM2 and the fifth rotation shaft TM5.

The first brake B1 is disposed between the seventh rotation shaft TM7and the transmission housing H, and causes the seventh rotation shaftTM7 to be operated as a selective fixed element.

The second brake B2 is disposed between the second rotation shaft TM2and the transmission housing H, and causes the second rotation shaft TM2to be operated as a selective fixed element.

The third brake B3 is disposed between the fourth rotation shaft TM4 andthe transmission housing H, and causes the fourth rotation shaft TM4 tobe operated as a selective fixed element.

The friction elements including the first, second, third, and fourthclutches C1, C2, C3, and C4 and the first, second, and third brakes B1,B2, and B3 may be multi-plate friction elements of a wet type that areoperated by hydraulic pressure.

FIG. 2 is an operation chart of friction elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention.

As shown in FIG. 2, three friction elements are operated at each speedstage in the planetary gear train according to various embodiments ofthe present invention. Shifting processes in the various embodiments ofthe present invention will be described in further detail.

A first forward speed stage D1 is achieved by simultaneous operation ofthe fourth clutch C4 and the first and third brakes B1 and B3. In astate that the second rotation shaft TM2 is connected to the fifthrotation shaft TM5 by operation of the fourth clutch C4, the input ismade into the first rotation shaft TM1, and the fourth and seventhrotation shafts TM4 and TM7 are operated as the fixed elements byoperation of the first and third brakes B1 and B3, the first forwardspeed stage D1 is achieved.

A second forward speed stage D2 is achieved by simultaneous operation ofthe second and fourth clutches C2 and C4 and the first brake B1. In astate that the second rotation shaft TM2 is connected to the first andfifth rotation shafts TM1 and TM5 by operation of the second and fourthclutches C2 and C4, the input is made into the first rotation shaft TM1,and the seventh rotation shaft TM7 is operated as the fixed element byoperation of the first brake B1, the second forward speed stage D2 isachieved.

A third forward speed stage D3 is achieved by simultaneous operation ofthe second clutch C2 and the first and third brakes B1 and B3. In astate that the first rotation shaft TM1 is connected to the secondrotation shaft TM2 by operation of the second clutch C2, the input ismade into the first rotation shaft TM1, and the fourth and seventhrotation shafts TM4 and TM7 are operated as the fixed elements byoperation of the first and third brakes B1 and B3, the third forwardspeed stage D3 is achieved.

A fourth forward speed stage D4 is achieved by simultaneous operation ofthe third clutch C3 and the first and third brakes B1 and B3. In a statethat the input shaft IS is connected to the eighth rotation shaft TM8 byoperation of the third clutch C3, the input is made into the first andeighth rotation shafts TM1 and TM8, and the fourth and seventh rotationshafts TM4 and TM7 are operated as the fixed elements by operation ofthe first and third brakes B1 and B3, the fourth forward speed stage D4is achieved.

A fifth forward speed stage D5 is achieved by simultaneous operation ofthe second and third clutches C2 and C3 and the third brake B3. In astate that the first rotation shaft TM1 is connected to the secondrotation shaft TM2 by operation of the second clutch C2, the input shaftIS is connected to the eighth rotation shaft TM8 by operation of thirdclutch C3, the input is made into the first and eighth rotation shaftsTM1 and TM8, and the second rotation shaft TM2 is operated as the fixedelement by operation of the third brake B3, the fifth forward speedstage D5 is achieved.

A sixth forward speed stage D6 is achieved by simultaneous operation ofthe second, third, and fourth clutches C2, C3, and C4. In a state thatthe second rotation shaft TM2 is connected to the first and fifthrotation shaft TM1 and TM5 by operation of the second and fourthclutches C2 and C4 and the input shaft IS is connected to the eighthrotation shaft TM8 by operation of the third clutch C3, the sixthforward speed stage D6 for just outputting the input is achieved as allof the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4 integrally rotate at the same speed.

A seventh forward speed stage D7 is achieved by simultaneous operationof the third and fourth clutches C3 and C4 and the third brake B3. In astate that the input shaft IS is connected to the eighth rotation shaftTM8 by operation of the third clutch C3, the second rotation shaft TM2is connected to the fifth rotation shaft TM5 by operation of the fourthclutch C4, the input is made into the first and eighth rotation shaftsTM1 and TM8, and the fourth rotation shaft TM4 is operated as the fixedelement by operation of the third brake B3, the seventh forward speedstage D7 is achieved.

An eighth forward speed stage D8 is achieved by simultaneous operationof the third and fourth clutches C3 and C4 and the second brake B2. In astate that the input shaft IS is connected the eighth rotation shaft TM8by operation of the third clutch C3, the second rotation shaft TM2 isconnected to the fifth rotation shaft TM5 by operation of the fourthclutch C4, the input is made into the first and eighth rotation shaftsTM1 and TM8, and the second rotation shaft TM2 is operated as the fixedelement by operation of the second brake B2, the eighth forward speedstage D8 is achieved.

A ninth forward speed stage D9 is achieved by simultaneous operation ofthe third clutch C3 and the second and third brakes B2 and B3. In astate that the input shaft IS is connected to the eighth rotation shaftTM8 by operation of the third clutch C3, the input is made into thefirst and eighth rotation shafts TM1 and TM8, and the second and fourthrotation shafts TM2 and TM4 are operated as the fixed elements byoperation of the second and third brakes B2 and B3, the ninth forwardspeed stage D9 is achieved.

A tenth forward speed stage D10 is achieved by simultaneous operation ofthe first and third clutches C1 and C3 and the second brake B2. In astate that the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6 by operation of the first clutch C1, and the inputshaft IS is connected to the eighth rotation shaft TM8 by operation ofthe third clutch C3, the input is made into the first and eighthrotation shafts TM1 and TM8, and the second rotation shaft TM2 isoperated as the fixed element by operation of the second brake B2, thetenth forward speed stage D10 is achieved.

A first reverse speed stage REV1 is achieved by simultaneous operationof the first, second, and third brakes B1, B2, and B3. In a state thatthe input is made into the first rotation shaft TM1, and the second,fourth, and seventh rotation shafts TM2, TM4, and TM7 are operated asthe fixed elements by operation of the first, second, and third brakesB1, B2, and B3, the first reverse speed stage REV1 is achieved.

A second reverse speed stage REV2 is achieved by simultaneous operationof the first and second brakes B1 and B2 and the first clutch C1. In astate that the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6 by operation of the first clutch C1, the input ismade into the first rotation shaft TM1, and the second and seventhrotation shafts TM2 and TM7 are operated as the fixed elements byoperation of the first and second brakes B1 and B2, the second reversespeed stage REV2 is achieved.

The planetary gear train according to various embodiments of the presentinvention may achieve ten forward speed stages and two reverse speedstages by control of four planetary gear sets PG1, PG2, PG3, and PG4with four clutches C1, C2, C3, and C4 and three brakes B1, B2, and B3.

In addition, engine driving efficiency may be maximized by achieving aspan of shift ratios to be greater than or equal to 9.0.

Further, drivability such as acceleration before and after the shift andrhythm of engine speed may be improved by almost linearly increasing ordecreasing step ratios between transmission steps.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train of an automatictransmission for a vehicle, comprising: an input shaft receiving torqueof an engine; an output shaft outputting changed torque of the engine; afirst planetary gear set including first, second, and third rotationelements; a second planetary gear set including fourth, fifth, and sixthrotation elements; a third planetary gear set including seventh, eighth,and ninth rotation elements; a fourth planetary gear set includingtenth, eleventh, and twelfth rotation elements; and seven frictionelements disposed to selectively connect the rotation elements with eachother and selectively connect the rotation elements with a transmissionhousing, wherein the input shaft is continuously connected to the firstrotation element, the output shaft is continuously connected to theeleventh rotation element, the third rotation element is continuouslyconnected to the fifth rotation element, the sixth rotation element iscontinuously connected to the seventh rotation element, the eighthrotation element is continuously connected to the eleventh rotationelement, the ninth rotation element is continuously connected to thetenth rotation element, and three friction elements among seven frictionelements are operated at each speed stage.
 2. The planetary gear trainof claim 1, wherein: the second rotation element is selectivelyconnected to the transmission housing, the fourth rotation element isselectively connected to the transmission housing, the ninth rotationelement is selectively connected to the transmission housing, the fourthrotation element is selectively connected to the output shaft, thetwelfth rotation element is selectively connected to the input shaft,and the sixth rotation element is selectively connected to the secondrotation element.
 3. The planetary gear train of claim 1, wherein: thefirst, second, and third rotation elements of the first planetary gearset are a sun gear, a planet carrier, and a ring gear, the fourth,fifth, and sixth rotation elements of the second planetary gear set area sun gear, a planet carrier, and a ring gear, the seventh, eighth, andninth rotation elements of the third planetary gear set are a sun gear,a planet carrier, and a ring gear, and the tenth, eleventh, and twelfthrotation elements of the fourth planetary gear set are a sun gear, aplanet carrier, and a ring gear.
 4. A planetary gear train of anautomatic transmission for a vehicle, comprising: an input shaftreceiving torque of an engine; an output shaft outputting changed torqueof the engine; a first planetary gear set including first, second, andthird rotation elements; a second planetary gear set including fourth,fifth, and sixth rotation elements; a third planetary gear set includingseventh, eighth, and ninth rotation elements; a fourth planetary gearset including tenth, eleventh, and twelfth rotation elements; sevenfriction elements disposed to selectively connect the rotation elementswith each other and selectively connect the rotation elements with atransmission housing; a first rotation shaft including the firstrotation element and directly connected to the input shaft; a secondrotation shaft including the second rotation element and selectivelyconnected to the first rotation shaft and the transmission housing; athird rotation shaft including the third and fifth rotation elements; afourth rotation shaft including the fourth rotation element andselectively connected to the transmission housing; a fifth rotationshaft including the sixth and seventh rotation elements and selectivelyconnected to the second rotation shaft; a sixth rotation shaft includingthe eighth and eleventh rotation elements and selectively connected tothe fourth rotation shaft, and directly connected to the output shaft; aseventh rotation shaft including the ninth and tenth rotation elementsand selectively connected to the transmission housing; and an eighthrotation shaft including the twelfth rotation element and selectivelyconnected to the input shaft.
 5. The planetary gear train of claim 4,wherein: the first planetary gear set is a single-pinion planetary gearset, in which the first rotation element is a first sun gear, the secondrotation element is a first planet carrier, and the third rotationelement is a first ring gear, the second planetary gear set is asingle-pinion planetary gear set, in which the fourth rotation elementis a second sun gear, the fifth rotation element is a second planetcarrier, and the sixth rotation element is a second ring gear, the thirdplanetary gear set is a single-pinion planetary gear set, in which theseventh rotation element is a third sun gear, the eighth rotationelement is a third planet carrier, and the ninth rotation element is athird ring gear, and the fourth planetary gear set is a single-pinionplanetary gear set, the tenth rotation element is a fourth sun gear, theeleventh rotation element is a fourth planet carrier, and the twelfthrotation element is a fourth ring gear.
 6. The planetary gear train ofclaim 4, wherein the seven friction elements comprise: a first clutchselectively connecting the fourth and sixth rotation shafts; a secondclutch selectively connecting the first and second rotation shafts; athird clutch selectively connecting the input shaft and the eighthrotation shaft; a fourth clutch selectively connecting the second andfifth rotation shafts; a first brake selectively connecting the seventhrotation shaft and the transmission housing; a second brake selectivelyconnecting the second rotation shaft and the transmission housing; and athird brake selectively connecting the fourth rotation shaft and thetransmission housing.
 7. The planetary gear train of claim 6, whereinshift speed stages achieved by selectively operating the seven frictionelements comprise: a first forward speed stage achieved by simultaneousoperation of the fourth clutch and the first and third brakes; a secondforward speed stage achieved by simultaneous operation of the second andfourth clutches and the first brake; a third forward speed stageachieved by simultaneous operation of the second clutch and the firstand third brakes; a fourth forward speed stage achieved by simultaneousoperation of the third clutch and the first and third brakes; a fifthforward speed stage achieved by simultaneous operation of the second andthird clutches and the third brake; a sixth forward speed stage achievedby simultaneous operation of the second, third and fourth clutches; aseventh forward speed stage achieved by simultaneous operation of thethird and fourth clutches and the third brake; an eighth forward speedstage achieved by simultaneous operation of the third and fourthclutches and the second brake; a ninth forward speed stage achieved bysimultaneous operation of the third clutch and the second and thirdbrakes; a tenth forward speed stage achieved by simultaneous operationof the first and third clutch and the second brake; a first reversespeed stage achieved by simultaneous operation of the first, second, andthird brakes; and a second reverse speed stage achieved by simultaneousoperation of the first clutch and the first and second brakes.
 8. Aplanetary gear train of an automatic transmission for a vehicle,comprising: an input shaft receiving torque of an engine; an outputshaft outputting changed torque of the engine; a first planetary gearset including first, second, and third rotation elements; a secondplanetary gear set including fourth, fifth, and sixth rotation elements;a third planetary gear set including seventh, eighth, and ninth rotationelements; a fourth planetary gear set including tenth, eleventh, andtwelfth rotation elements; a first rotation shaft including the firstrotation element and directly connected to the input shaft; a secondrotation shaft including the second rotation element and selectivelyconnected to the first rotation shaft and the transmission housing; athird rotation shaft including the third and fifth rotation elements; afourth rotation shaft including the fourth rotation element andselectively connected to the transmission housing; a fifth rotationshaft including the sixth and seventh rotation elements and selectivelyconnected to the second rotation shaft; a sixth rotation shaft includingthe eighth and eleventh rotation elements and selectively connected tothe fourth rotation shaft, and directly connected to the output shaft; aseventh rotation shaft including the ninth and tenth rotation elementsand selectively connected to the transmission housing; an eighthrotation shaft including the twelfth rotation element and selectivelyconnected to the input shaft; a first clutch selectively connected tofourth and sixth rotation shafts; a second clutch selectively connectedto the first and second rotation shafts; a third clutch selectivelyconnected to the input shaft and the eighth rotation shaft; a fourthclutch selectively connected to the second and fifth rotation shafts; afirst brake selectively connected to the seventh rotation shaft and thetransmission housing; a second brake selectively connected to the secondrotation shaft and the transmission housing; and a third brakeselectively connected to the fourth rotation shaft and the transmissionhousing.
 9. The planetary gear train of claim 8, wherein: the firstplanetary gear set is a single-pinion planetary gear set, in which thefirst rotation element is a first sun gear, the second rotation elementis a first planet carrier, and the third rotation element is a firstring gear, the second planetary gear set is a single-pinion planetarygear set, in which the fourth rotation element is a second sun gear, thefifth rotation element is a second planet carrier, and the sixthrotation element is a second ring gear, the third planetary gear set isa single-pinion planetary gear set, in which the seventh rotationelement is a third sun gear, the eighth rotation element is a thirdplanet carrier, and the ninth rotation element is a third ring gear, andthe fourth planetary gear set is a single-pinion planetary gear set, thetenth rotation element is a fourth sun gear, the eleventh rotationelement is a fourth planet carrier, and the twelfth rotation element isa fourth ring gear.
 10. The planetary gear train of claim 8, whereinshift speed stages achieved by selectively operating the first, second,third, and fourth clutches and the first, second, and third brakescomprise: a first forward speed stage achieved by simultaneous operationof the fourth clutch and the first and third brakes; a second forwardspeed stage achieved by simultaneous operation of the second and fourthclutches and the first brake; a third forward speed stage achieved bysimultaneous operation of the second clutch and the first and thirdbrakes; a fourth forward speed stage achieved by simultaneous operationof the third clutch and the first and third brakes; a fifth forwardspeed stage achieved by simultaneous operation of the second and thirdclutches and the third brake; a sixth forward speed stage achieved bysimultaneous operation of the second, third and fourth clutches; aseventh forward speed stage achieved by simultaneous operation of thethird and fourth clutches and the third brake; an eighth forward speedstage achieved by simultaneous operation of the third and fourthclutches and the second brake; a ninth forward speed stage achieved bysimultaneous operation of the third clutch and the second and thirdbrakes; a tenth forward speed stage achieved by simultaneous operationof the first and third clutch and the second brake; a first reversespeed stage achieved by simultaneous operation of the first, second, andthird brakes; and a second reverse speed stage achieved by simultaneousoperation of the first clutch and the first and second brakes.